Quite different from the traditional linear polymer in structure, the dendritic polymer has a highly-ordered three-dimensional structure, consists of an initiator core, an inner-layer repeating unit and an outer-layer end group, and is featured by a high degree of geometric symmetry, a precise molecular structure, as well as a large number of surface functional groups and internal cavities. However, it often takes an extremely long time to prepare a perfect dendritic polymer, so that the application of the dendritic polymer is limited, and the dendritic polymer is generally quite high in price due to the difficulty in preparation. Compared to the dendritic polymer, the hyperbranched polymer has an irregular three-dimensional quasi-spherical structure, the molecule contains a part of linear structural units, and the functional group is partially located on the surface of the molecule and partially present inside of the molecule; the hyperbranched polymer has a wide molecular weight distribution and a degree of branching between 0 and 1. Although the hyperbranched polymer is not as perfect as the dendritic polymer in structure, the physical and chemical properties of the hyperbranched polymer are very similar to those of the dendritic polymer, such as a good solubility, a small solution and melt viscosity, and a plurality of end functional groups and intramolecular voids. Besides, the hyperbranched polymer also has its own advantages, for example, the synthesis process is simple, and it can be synthesized in one step. It is entirely possible that, the hyperbranched polymer can replace the dendritic polymer in aspects, such as a drug carrier and a polymer catalyst, a curing agent, a solvent-free coating and a polymer processing aid for development and application.
Up to now, there are mainly four preparation methods for the hyperbranched polymer, that is, condensation polymerization reaction, addition polymerization reaction, self-condensing vinyl polymerization (SCVP) and ring-opening polymerization. Particularly, the most mature method is that, the hyperbranched polymer is prepared by condensation polymerization reactions of AB2 type monomers, and the method has universality and practicability. However, the AB2 type monomer has not currently been commercialized yet, and the only several types of AB2 monomer on the market are not sufficient to meet all the demands, and preparing the hyperbranched polymer by polymerization reactions of A2+B3 type monomers has attracted people's attention. Since A2 reacts with B3, gelation reaction easily occurs in the preparation process, and it is necessary to control the reaction by controlling the reaction time, the reaction proportion and the reaction temperature.
Currently, there is a rare case where main chains of polyether ester hyperbranched polymers contain rigid aromatic groups and flexible aliphatic alkyl chains simultaneously. However, such a unique combination often brings many distinctive properties to the polymer. If the hyperbranched polymer contains a large number of aromatic groups, excessively strong rigidity will lead to a large space steric effect, thereby significantly reducing its usability. The rigidity and flexibility of the hyperbranched polymer can be well regulated by introducing aromatic groups and aliphatic chains into the hyperbranched polymer at the same time. The presence of the flexible segment can effectively reduce the space steric effect and make the effect more efficient; while the rigid groups in the backbone can improve the glass transition temperature (Tg) greatly, and provide excellent processing and mechanic properties.